/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.db.engine.modification.utils;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.io.UncheckedIOException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * Copied from {@link java.io.BufferedReader}, trace the read position by modifying the fill()
 * method.
 */
public class TracedBufferedReader extends Reader {
    private Reader in;

    private char cb[];
    private int nChars, nextChar;

    private static final int INVALIDATED = -2;
    private static final int UNMARKED = -1;
    private int markedChar = UNMARKED;
    private int readAheadLimit = 0; /* Valid only when markedChar > 0 */

    /**
     * If the next character is a line feed, skip it
     */
    private boolean skipLF = false;

    /**
     * The skipLF flag when the mark was set
     */
    private boolean markedSkipLF = false;

    private static int defaultCharBufferSize = 8192;
    private static int defaultExpectedLineLength = 80;

    /**
     * the total bytes number already filled into cb
     */
    private long totalFilledBytesNum = 0;

    /**
     * Creates a buffering character-input stream that uses an input buffer of the specified size.
     *
     * @param in A Reader
     * @param sz Input-buffer size
     * @throws IllegalArgumentException If {@code sz <= 0}
     */
    public TracedBufferedReader(Reader in, int sz) {
        super(in);
        if (sz <= 0) {
            throw new IllegalArgumentException("Buffer size <= 0");
        }
        this.in = in;
        cb = new char[sz];
        nextChar = nChars = 0;
    }

    /**
     * Creates a buffering character-input stream that uses a default-sized input buffer.
     *
     * @param in A Reader
     */
    public TracedBufferedReader(Reader in) {
        this(in, defaultCharBufferSize);
    }

    /**
     * Checks to make sure that the stream has not been closed
     */
    private void ensureOpen() throws IOException {
        if (in == null) {
            throw new IOException("Stream closed");
        }
    }

    /**
     * {@link BufferedReader#fill()}
     */
    private void fill() throws IOException {
        int dst;
        if (markedChar <= UNMARKED) {
            /* No mark */
            dst = 0;
        } else {
            /* Marked */
            int delta = nextChar - markedChar;
            if (delta >= readAheadLimit) {
                /* Gone past read-ahead limit: Invalidate mark */
                markedChar = INVALIDATED;
                readAheadLimit = 0;
                dst = 0;
            } else {
                if (readAheadLimit <= cb.length) {
                    /* Shuffle in the current buffer */
                    System.arraycopy(cb, markedChar, cb, 0, delta);
                    markedChar = 0;
                    dst = delta;
                } else {
                    /* Reallocate buffer to accommodate read-ahead limit */
                    char ncb[] = new char[readAheadLimit];
                    System.arraycopy(cb, markedChar, ncb, 0, delta);
                    cb = ncb;
                    markedChar = 0;
                    dst = delta;
                }
                nextChar = nChars = delta;
            }
        }

        int n;
        do {
            n = in.read(cb, dst, cb.length - dst);
        } while (n == 0);
        if (n > 0) {
            nChars = dst + n;
            nextChar = dst;
            totalFilledBytesNum = totalFilledBytesNum + n;
        }
    }

    /**
     * {@link BufferedReader#read()}
     */
    @Override
    public int read() throws IOException {
        synchronized (lock) {
            ensureOpen();
            for (; ; ) {
                if (nextChar >= nChars) {
                    fill();
                    if (nextChar >= nChars) {
                        return -1;
                    }
                }
                if (skipLF) {
                    skipLF = false;
                    if (cb[nextChar] == '\n') {
                        nextChar++;
                        continue;
                    }
                }
                return cb[nextChar++];
            }
        }
    }

    /**
     * {@link BufferedReader#read1(char[], int, int)}
     */
    private int read1(char[] cbuf, int off, int len) throws IOException {
        if (nextChar >= nChars) {
      /* If the requested length is at least as large as the buffer, and
      if there is no mark/reset activity, and if line feeds are not
      being skipped, do not bother to copy the characters into the
      local buffer.  In this way buffered streams will cascade
      harmlessly. */
            if (len >= cb.length && markedChar <= UNMARKED && !skipLF) {
                return in.read(cbuf, off, len);
            }
            fill();
        }
        if (nextChar >= nChars) {
            return -1;
        }
        if (skipLF) {
            skipLF = false;
            if (cb[nextChar] == '\n') {
                nextChar++;
                if (nextChar >= nChars) {
                    fill();
                }
                if (nextChar >= nChars) {
                    return -1;
                }
            }
        }
        int n = Math.min(len, nChars - nextChar);
        System.arraycopy(cb, nextChar, cbuf, off, n);
        nextChar += n;
        return n;
    }

    /**
     * {@link BufferedReader#read(char[], int, int)}
     */
    @Override
    public int read(char cbuf[], int off, int len) throws IOException {
        synchronized (lock) {
            ensureOpen();
            if ((off < 0)
                    || (off > cbuf.length)
                    || (len < 0)
                    || ((off + len) > cbuf.length)
                    || ((off + len) < 0)) {
                throw new IndexOutOfBoundsException();
            } else if (len == 0) {
                return 0;
            }

            int n = read1(cbuf, off, len);
            if (n <= 0) {
                return n;
            }
            while ((n < len) && in.ready()) {
                int n1 = read1(cbuf, off + n, len - n);
                if (n1 <= 0) {
                    break;
                }
                n += n1;
            }
            return n;
        }
    }

    /**
     * {@link BufferedReader#readLine(boolean)}
     */
    String readLine(boolean ignoreLF) throws IOException {
        StringBuilder s = null;
        int startChar;

        synchronized (lock) {
            ensureOpen();
            boolean omitLF = ignoreLF || skipLF;

            bufferLoop:
            for (; ; ) {

                if (nextChar >= nChars) {
                    fill();
                }
                if (nextChar >= nChars) {
                    /* EOF */
                    if (s != null && s.length() > 0) {
                        return s.toString();
                    } else {
                        return null;
                    }
                }
                boolean eol = false;
                char c = 0;
                int i;

                /* Skip a leftover '\n', if necessary */
                if (omitLF && (cb[nextChar] == '\n')) {
                    nextChar++;
                }
                skipLF = false;
                omitLF = false;

                charLoop:
                for (i = nextChar; i < nChars; i++) {
                    c = cb[i];
                    if ((c == '\n') || (c == '\r')) {
                        eol = true;
                        break charLoop;
                    }
                }

                startChar = nextChar;
                nextChar = i;

                if (eol) {
                    String str;
                    if (s == null) {
                        str = new String(cb, startChar, i - startChar);
                    } else {
                        s.append(cb, startChar, i - startChar);
                        str = s.toString();
                    }
                    nextChar++;
                    if (c == '\r') {
                        skipLF = true;
                        if (read() != -1) {
                            nextChar--;
                        }
                    }
                    return str;
                }

                if (s == null) {
                    s = new StringBuilder(defaultExpectedLineLength);
                }
                s.append(cb, startChar, i - startChar);
            }
        }
    }

    /**
     * {@link BufferedReader#readLine()}
     */
    public String readLine() throws IOException {
        return readLine(false);
    }

    /**
     * {@link BufferedReader#skip(long)}
     */
    @Override
    public long skip(long n) throws IOException {
        if (n < 0L) {
            throw new IllegalArgumentException("skip value is negative");
        }
        synchronized (lock) {
            ensureOpen();
            long r = n;
            while (r > 0) {
                if (nextChar >= nChars) {
                    fill();
                }
                if (nextChar >= nChars) {
                    /* EOF */
                    break;
                }
                if (skipLF) {
                    skipLF = false;
                    if (cb[nextChar] == '\n') {
                        nextChar++;
                    }
                }
                long d = nChars - nextChar;
                if (r <= d) {
                    nextChar += r;
                    r = 0;
                    break;
                } else {
                    r -= d;
                    nextChar = nChars;
                }
            }
            return n - r;
        }
    }

    /**
     * {@link BufferedReader#ready()}
     */
    @Override
    public boolean ready() throws IOException {
        synchronized (lock) {
            ensureOpen();

            /*
             * If newline needs to be skipped and the next char to be read
             * is a newline character, then just skip it right away.
             */
            if (skipLF) {
                /* Note that in.ready() will return true if and only if the next
                 * read on the stream will not block.
                 */
                if (nextChar >= nChars && in.ready()) {
                    fill();
                }
                if (nextChar < nChars) {
                    if (cb[nextChar] == '\n') {
                        nextChar++;
                    }
                    skipLF = false;
                }
            }
            return (nextChar < nChars) || in.ready();
        }
    }

    /**
     * {@link BufferedReader#markSupported()}
     */
    @Override
    public boolean markSupported() {
        return true;
    }

    /**
     * {@link BufferedReader#mark(int)}
     */
    @Override
    public void mark(int readAheadLimit) throws IOException {
        if (readAheadLimit < 0) {
            throw new IllegalArgumentException("Read-ahead limit < 0");
        }
        synchronized (lock) {
            ensureOpen();
            this.readAheadLimit = readAheadLimit;
            markedChar = nextChar;
            markedSkipLF = skipLF;
        }
    }

    /**
     * {@link BufferedReader#reset()}
     */
    @Override
    public void reset() throws IOException {
        synchronized (lock) {
            ensureOpen();
            if (markedChar < 0) {
                throw new IOException((markedChar == INVALIDATED) ? "Mark invalid" : "Stream not marked");
            }
            nextChar = markedChar;
            skipLF = markedSkipLF;
        }
    }

    /**
     * {@link BufferedReader#close()}
     */
    @Override
    public void close() throws IOException {
        synchronized (lock) {
            if (in == null) {
                return;
            }
            try {
                in.close();
            } finally {
                in = null;
                cb = null;
            }
        }
    }

    /**
     * {@link BufferedReader#lines()}
     */
    public Stream<String> lines() {
        Iterator<String> iter =
                new Iterator<String>() {
                    String nextLine = null;

                    @Override
                    public boolean hasNext() {
                        if (nextLine != null) {
                            return true;
                        } else {
                            try {
                                nextLine = readLine();
                                return (nextLine != null);
                            } catch (IOException e) {
                                throw new UncheckedIOException(e);
                            }
                        }
                    }

                    @Override
                    public String next() {
                        if (nextLine != null || hasNext()) {
                            String line = nextLine;
                            nextLine = null;
                            return line;
                        } else {
                            throw new NoSuchElementException();
                        }
                    }
                };
        return StreamSupport.stream(
                Spliterators.spliteratorUnknownSize(iter, Spliterator.ORDERED | Spliterator.NONNULL),
                false);
    }

    /**
     * Returns this reader's file position.
     *
     * @return This reader's file position, a non-negative integer counting the number of bytes from
     * the beginning of the file to the current position
     */
    public long position() {
        // position = totalFilledBytesNum - lastFilledBytesNum + readOffsetInLastFilledBytes
        // lastFilledBytesNum = nChars - dst, readOffsetInLastFilledBytes = nextChar - dst
        return totalFilledBytesNum - nChars + nextChar;
    }
}
